The present invention relates to an actuator which can be actuated along a longitudinal axis, in particular for a spring carrier.
Linear actuators are employed in a large number of appliances. Often there is the problem that a component which is to be driven by the actuator is subjected to a load acting parallel to the direction of actuation. As a result, the components of the actuator are subjected to severe loading, even when the actuator is not being operated. In many cases, these actuators must even actively apply a continuous holding force in order to counteract the load and prevent unwanted adjustment.
The problems can be illustrated clearly using a spring carrier in a wheel suspension system of a vehicle. Spring carriers of this kind often have a coil spring which is arranged between two spring plates and the preload of which can be set by axial movement of one of the spring plates. In this way, the spring force is influenced by a displacement of the spring characteristic in order then to be able to regulate the level of the vehicle. In order to move the spring plate, the usual practice is to use an actuator comprising an electric motor and a threaded spindle which interacts with a threaded nut connected to the spring plate.
The wheel loads of the vehicle act in the longitudinal direction of the spring carrier. These loads are transmitted at least partially via the threaded nut and the threaded spindle and hence via the actuator. Because they are subjected continuously to static and dynamic loads, the components of the actuator must be of correspondingly robust dimensions. Moreover, there is a need for the presence of devices which prevent unwanted movement of the spring plate by the wheel loads. In individual cases, additional brakes or switchable double overrunning clutches are provided for this purpose. Moreover, there is a need for a “fail-safe” configuration of such devices, for safety reasons among others. They must be controlled separately and may require their own energy supply. A holding force counteracting the unwanted displacement can also be provided by the electric motor itself but this results in high energy consumption.
It is an object of the invention to provide an actuator of the type stated at the outset which reliably permits axial movement and at the same time provides a supporting or locking function which at least partially relieves the actuator of loads when it is not being operated. The intention is that the actuator should be compact and inexpensive and provide the abovementioned functions without additional energy supply systems.